Tool holder

ABSTRACT

A tool holder is provided with vibration dampening means to eliminate chatter marks recorded on workpieces by a cutting tool attached thereto. The vibration dampening characteristics are provided by a high density member located within a longitudinal cavity in the tool holder. The dampening element moves in a direction which counters the normal resonant frequency cutting vibrations generated in the tool holder.

United States Patent Maddux Nov. 27, 1973 TOOL HOLDER [75] Inventor:Kenneth Carl Maddux, Cincinnati. Prim? Emmi'le-Duane A Regs OhioAttorney-Robert L. Lehmann et al.

[73] Assignee: N L Industries, Inc., New York.

New York 7] ABSTRACT [22] Fil d; A 19, 1972 A tool holder is providedwith vibration dampening Appl. No.: 245,329

means to eliminate chatter marks recorded on workpieces by a cuttingtool attached thereto. The vibration dampening characteristics areprovided by a high density member located within a longitudinal cavityin the tool holder. The dampening element moves in a direction whichcounters the normal resonant frequency cutting vibrations generated inthe tool holder.

4 Claims, 2 Drawing Figures root notnnri BACKGROUND OF THE INVENTION Anyvibratory motion between a cutting tool and workpiece will be recordedon the workpiece surface which may result in an unsatisfactory surfacefinish. Dimensional accuracy, tool life and machine life may also beadversly affected.

The causes of chatter can be traced to a static or dynamic structuralweakness in the machine tool, workpiece, metal cutting system. Thedeflection of the cutting tool system in many cases is the major causeof chatter since the tool holder will vibrate at its resonant frequency.In cutting systems for boring very deep or narrow holes, the cuttingtool is mounted on a tool holder commonly referred to as a boring bar.These bars tend to be elongated and slender and tend to be rather easilyexcited or vibrated at their resonant frequency. Vibrations aretransmitted to the workpiece via the cutting tool. A resultant chatterpattern is left on the workpiece, and in more extensive cases a hole maybe so improperly cut as to render the workpiece worthless.

Several attempts have been made to perfect a tool holder which possessesadequate vibration dampening characteristics. One such attempt involvesthe use of sliding disks which, enclosed within the tool holder, move soas to counter the self excited vibrations in the tool holder dissipatingthe vibratory energy through friction losses.

The instant invention provides a unique concept in vibration dampening.The use of a high density member effectively dampens vibrationsgenerated in the tool holder. Additionally, the system hereinafterdescribed is adjustable so as to provide highly effective dampening overa range of frequencies. In addition to its superior dampeningproperties, the instant invention is very competitive, cost-wise, tomanufacture.

SUMMARY OF THE INVENTION A primary object of the present invention isthe pro vision of a tool holder of superior vibration dampeningcharacteristics.

Another object of the present invention is the provision of tool holdercapable of dampening cutting vibrations within a range of resonantfrequencies.

Yet another object of the present invention is the provision of a toolholder with superior dampening characteristics which is inexpensive tomanufacture.

In accordance with the above designs, the present invention ispreferredly embodied in a tool holder which includes vibration dampeningmeans enclosed within a longitudinal cavity formed in the holder. Anelongated, high density vibration dampening member is disposed withinthe cavity, which member is movable therewithin. As the tool holdervibrates during metal cutting, the dampening member moves universallywithin the tool holder. That movement causes forces which oppose thevibrations generated in the tool holder, effectively eliminating chatteron the workpiece due to the tool holder instability. Also providedwithin the cavity are resilient means urging the dampening membertowards its non-vibratory state. The resilient means serves to transfercounter-vibrational forces to the tool holder, as well as to urge thedampening member toward its non-vibratory state.

Also provided in this system is an adjusting means. This means serves toeither increase or decrease, be tween a maximum and minimum, thedampening frequency. As each resonant frequency of vibration requires aspecific movement of the dampening member, with a simple adjustment, asingle: tool holder embodying the structure hereinafter describedeffectively dampens all resonant vibration frequencies within a givenrange.

DESCRIPTION OF THE DRAWINGS FIG. I illustrates a cross-sectional view ofa preferred embodiment of the present invention.

FIGQZ illustrates a cross-sectional view of an alternate embodiment ofthe present invention.

DETAILED DESCRIPTION Referring to FIG. I, the present invention isembodied in a tool holder 10 such as a boring bar used for boring deepholes in workpieces. A cutting tool (not shown) can be mounted atsection l2 which tool will bore a hole in a workpiece as it and the toolholder 10 enter the workpiece. The cutting dynamics produce resonantfrequency vibrations which travel through the tool holder l0 affectingthe stability of the cutting process. For this reason the tool holder I0is provided with vibration dampening means M which will dampen theresonant frequency vibrations generated in the tool holder.

The vibration dampening means M is carried within the cavity 116 whichis formed in the body of the tool holder Ill. The dampening propertiesof the instant invention are accomplished by the dampening member lb.This member lb is elongated and has tapered ends 20, 22 which terminateat the flat transverse faces 24, 26. As shown, the body of member 11% isgenerally cylindrical there being clearance between the cavity 16 andthe cylindrical body. It has been found that a dampening member of highdensity, such as a heavy metal is uniquely suited in this design foreffective vibration dampening. Furthermore, depleted or spent uraniumprovides exceptionally efiective dampening and at the same time rendersthis material, which has previously been waste material subject ofdifficult disposition, uniquely useful.

Located within, and at the opposing ends thereof, are the front and rearretaining blocks denoted as 2% and 3b. These blocks 2% and 311) eachhave a central chamber 32, 341 which is conical in shape, the elementsof which are generally parallel to the elements of the tapered sections20, 22. As here shown the blocks 2%., 30 are aligned such that thechambers 32, 1% are open to each other. The chambers 32, 343 enclose thedampening member id, but do not make srface contact therewith. Surfacecontact is prohibitted by the use of urging means, or resilient members3%,. db, known ocmmonly as ll rings, which are fitted about grooves A12,44 formed in the tapered sections 2t), 22 of member 118.

In actual operation the vibration dampening is accomplished by theuniversal movement of the dampening member lb. Vibrations transferred tothe tool holder lll travel throughtout the tool holder. These vibrationscause tool holder to flex or bend which can result in chatter marksrecorded on a workpiece, or an improperly drilled hole. As a vibrationpasses through the tool holder III the dampening member lid will move orbounce, in a direction which tends to counter the vibrational force. Thedampening member 13 variously compresses resilient members 33, 44)between itself and chambers 32, 34. This interaction represents atransfer of forces to the tool holder lit), which forces generallyoppose the vibrational forces present at that time in the tool holder.The net effect is a vector sum of zero vibra tional forces present inthe tool holder. in other words the tool holder is prohibited frombending, and as a result, chatter marks will not be recorded on theworkpiece surface. Additionally, long thin holes can now be easily cutwithout fear that excessive bending will break a thin tool holder.

The choice of a heavy metal for this task provides obvious benefits. Alarge counter vibrational force can be exerted with a small sizeddampening member 118. Also, a heavy member is able to produce aconsiderable force with only a small movement. As previously stated,depleted uranium is uniquely adapted for this use. As one of theheaviest substances per unit volume it provides excellent vibrationdampening. Heretofore, it has been almost exclusively a waste materialin search for methods of disposal. in the environment of the instantinvention it becomes a valuable substance.

At this point attention is turned to the resilient members 33, 4MP whichare fit about grooves 42, 414 formed in tapered sections 2d, 22. At alltimes these resilient members are in contact with the walls of chambers32, 34. This means that member 118 is not free to bounce off the wallsof the chambers but rather its movement is confined to the universaltravel permitted by the compressed resilient members 38, 40. As themember 18 moves toward chamber 32 it compresses resilient member 38.. inaccordance with the strength of the causative vibration, that resilientmember will be compressed only so much as needed to halt the thrust ofmember 118. At the same time resilient member 40) is relaxed to the samedegree that member 38 is compressed. As a result, resilient member 38now acts on member l8 thrusting it back toward its undampened condition,thereby relaxing its compression to the same degree that resilientmember 40 is compressed. in such a manner the dampening means 114 isreadied to dampen the next vibration excited by the cutting tool, thesequence of movements being similar. The member 18 also moves with upand down motion. The sequence of spring compression and depression isessentially the same as that for horizontal movement. At all timesduring the hereinbefore described movements, the resilient members arein contact with their respective chamber 32, 341 walls. in fact, thesemembers actually suspend member 113 which does not touch, at all, thewalls of cavity 16 but rather bounces within the prohib' ited movementallowed by the resilient members 38, 4b.

The invention thus far described will provide effective dampening foronly a single vibration frequency. Obviously, it is desirable for asingle tool holder to be effective over a range of frequencies. in otherwords, a method must be provided which will adjust the compression ofresilient members 38, 4h. This objective is accomplished by renderingthe rear retaining block 30 movable. As block 3613 is urged toward fixedblock 28, the resilient members 38 and 441i are compressed. Thiscompression renders the dampening means effective for dampening highfrequency vibrations as the members 38, 40 provide greater thrust forceson member 118. As block 30 is moved away from block 23, the compressionof resilient members 38, 40 is relaxed rendering the dampening means Meffective for dampening low frequency vibrations since the thrust forcespro vided by resilient members 38, 44B is now quite low, and thepermitted travel of member H8 is fairly large. The dampening means isthen effective for dampening, between a specified maximum and minimumvibration frequency. These limits are determined by size and diameter ofmember 18, resiliency of the 0 rings, and the material chosen for use asthe dampening member. Obviously, the minimum frequency is that at whichthe resilient members just touch the blocks 28, 30. On the other hand,the maximum frequency that can be dampened coincides with the situationwhere the compression in the resilient members 38, 40 is so great thatthe member 18 is rendered virtually immobile.

The adjustability charactaristic of retaining block 30 is accomplishedby the provision of an adjusting means 46. A'hole 48 is formed in thetool holder body 10 at an acute angle to the tool holder axis. That hole48 is partially threaded 53 and is counterbored 52. A screw 54 isreceived in the hole 48 and threadably engages at section 50 such thatthe tip 56 of that screw extends into the cavity 16. The tip of screw 54contacts the slide surface 53 of block 30 at section 60. As the screw 54is rotated, the tip 56 slides up or down along surface 58 and adjuststhe position of block 3%. As the screw 54 travels out of that hole, theresilient members are relaxed. Thus, the adjustments necessary toestablish a particular dampening frequency are simply carried out.

Referring to FIG. 2, an alternative adjusting means 46 is shown. Therear retaining block 30 has an angular slide surface 62 formed thereon.A wedge or guide 64 by means of slide surface 66, slides along surface62. An access hole 68 is formed in body and extends completely throughthat body, which hole also extends through guide 64. A screw 7th extendsthrough the hole 68 (including the guide), and only the hole in theguide 64 is threaded. As the screw 7b is turned the guide 64 moves up ordown the screw '70, which screw does not move vertically within the hole68. As the guide 64 moves, so moves the retaining block 30 therebyadjusting the dampening frequency.

in both adjusting embodiments the rear retaining block 3% is moved to aposition at which it will dampen at the resonant vibration frequency ofthe boring bar 113. Each bar will vibrate at certain frequency,irrespective of cutting speed, dependent only upon the position at whichthe bar is held along its length. in other words, the greater the barlength the lower will be the resonant vibration frequency and conversly,the shorter the bar length, the higher the vibration frequency.Therefore, the instant invention is effective to dampen resonantfrequencies which will vary in accordance with the positioning of thebar in a tool stand.

Another aspect of the present invention is the provision of a monitoringmeans to indicate the particular dampening setting. For such a functionthe hole 72 is formed in body 10 and is adjacent block 34]). A groove'74 is formed on block 30 and is visible through window '73. Theposition of groove 74 indicates the vibration dampening frequency of thedampening means 14 for any particular adjusting means 46 setting.

As has been seen, the present invention provides a highly useful andefficient way of eliminating chatter in a cutting process. it ischaractarized by an economy of moving parts as well as relative ease ofmanufacture and use. It is highly effective in performing its primaryfunction, that of vibration dampening, enabling the production ofchatter-free workpieces. Additionally, it provides a use for whatheretofore has been a waste material of difficult disposition.

It is obvious that many variations may be made in the details of theinstant invention without departing from the spirit and scope of theappended claims.

What is claimed is:

ll. A tool holder comprising a supporting body having an elongatedcylindrical cavity therein of substantially uniform diameter, a portionof said body being constructed and arranged to support a tool, vibrationdampening means for dampening vibrations transferred to said body bysaid tool, said vibration dampening means comprising an elongatedsubstantially cylindrical dampening member formed of relatively highdensity material each end of said dampening member being tapered, saiddampening member being dimensioned to have substantially universalmovement within said cav ity in directions to counter vibrations of saidtool holder, and mounting means arranged at opposite ends, respectively,of said cavity for mounting said dampening member therein in a manner totransmit the counter vibration movements of said dampening member tosaid tool holder, said mounting means comprising first and secondtlcylindrical blocks corresponding in diameter to the diameter of saidcylindrical cavity, each block having an inwardly facing frusto-conicalcavity,

one of said blocks being fixed in said cylindrical cavity and the secondblock being arranged to move longitudinally therein, said blocks spacedapart sufficiently to accomodate the tapered ends of said dampeningmember in the respective frusto-coniical cavities of said blocks, andresilient means circumscribing the tapered ends of said dampening memberarranged to support said tampered ends in said frustoconical cavities inspaced relationship thereto.

2. A tool holder according to claim 11, wherein each tapered end of saiddampening member is provided with an annular groove and said resilientmeans comprises an 0 ring mounted in the annular groove.

3. A tool holder according to claim 2, wherein vibration frequencyadjusting means is mounted in said tool holder in cooperative engagementwith said movable block for moving the latter longitudinally in saidcavity thereby to vary the compression of the resilient means mountedbetween the tapered ends of said dampening member and the correspondingfrusto-conical cavities of said mounting blocks in accordance withmaximum and minimum vibration frequencies of said tool holder.

4. A tool holder according to claim 3 wherein said adjustable secondblock is provided with an index mark and said tool holder is providedwith a sight-aperture arranged to afford a view of the index mark ofsaid adjusable block for monitoring vibration frequency settings of saiddampening member.

1. A tool holder comprising a supporting body having an elongatedcylindrical cavity therein of substantially uniform diameter, a portionof said body being constructed and arranged to support a tool, vibrationdampening means for dampening vibrations transferred to said body bysaid tool, said vibration dampening means comprising an elongatedsubstantially cylindrical dampening member formed of relatively highdensity material each end of said dampening member being tapered, saiddampening member being dimensioned to have substantially universalmovement within said cavity in directions to counter vibrations of saidtool holder, and mounting means arranged at opposite ends, respectively,of said cavity for mounting said dampening member therein in a manner totransmit the counter vibration movements of said dampening member tosaid tool holder, said mounting means comprising first and second0cylindrical blocks corresponding in diameter to the diameter of saidcylindrical cavity, each block having an inwardly facing frusto-conicalcavity, one of said blocks being fixed in said cylindrical cavity andthe second block being arranged to move longitudinaLly therein, saidblocks spaced apart sufficiently to accomodate the tapered ends of saiddampening member in the respective frusto-conical cavities of saidblocks, and resilient means circumscribing the tapered ends of saiddampening member arranged to support said tampered ends in saidfrustoconical cavities in spaced relationship thereto.
 2. A tool holderaccording to claim 1, wherein each tapered end of said dampening memberis provided with an annular groove and said resilient means comprises an''''0'''' ring mounted in the annular groove.
 3. A tool holder accordingto claim 2, wherein vibration frequency adjusting means is mounted insaid tool holder in cooperative engagement with said movable block formoving the latter longitudinally in said cavity thereby to vary thecompression of the resilient means mounted between the tapered ends ofsaid dampening member and the corresponding frusto-conical cavities ofsaid mounting blocks in accordance with maximum and minimum vibrationfrequencies of said tool holder.
 4. A tool holder according to claim 3wherein said adjustable second block is provided with an index mark andsaid tool holder is provided with a sight-aperture arranged to afford aview of the index mark of said adjusable block for monitoring vibrationfrequency settings of said dampening member.